The invention relates to novel catalysts and to the preparation thereof and also to the preferred use thereof in the production of polyisocyanate polyaddition products.
Polyurethanes have long been known and are employed in many fields. Frequently the actual polyurethane reaction has to be carried out using catalysts, since otherwise the reaction proceeds too slowly and, in appropriate circumstances, results in polyurethane products with poor mechanical properties. In most cases, the reaction between the hydroxyl component and the NCO component has to be catalysed. In the case of the customary catalysts, a distinction is made between metalliferous and non-metalliferous catalysts. Typical customary catalysts are, for example, amine catalysts such as, for instance, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO) or triethanolamine. In the case of metalliferous catalysts, it is usually a question of Lewis-acid compounds, such as, for instance, dibutyltin dilaurate, lead octoate, tin octoate, titanium and zirconium complexes, but also cadmium compounds, bismuth compounds (for example, bismuth neodecanoate) and iron compounds. One requirement placed upon the catalyst is that it catalyses, in as defined a manner as possible, only one of the diverse polyurethane reactions, such as, for instance, only the reaction between OH groups and NCO groups. Side reactions—such as, for example, dimerisations or trimerisations of the isocyanate, allophanatisations, biuretisations, water reactions or formations of urea—should not be catalysed in the course of this one reaction. The requirement is always to the effect that an optimal catalyst catalyses precisely the reaction that is desired—for example, only the water reaction—so that a defined foam profile arises or, as in the case where use is made of the potassium acetates, preferably the polyisocyanurate reaction. Hitherto, however, there have hardly been any catalysts that catalyse only one defined reaction. But this is extremely desirable precisely in the case of the diverse reaction possibilities in the preparation of polyurethane. Of particular interest are not only catalysts that catalyse only one reaction in defined manner but catalysts that additionally become selectively active and catalyse reactions only under certain conditions. In such cases, one speaks of switchable catalysts. These switchable catalysts are, in turn, subdivided into thermally, photochemically or optically switchable catalysts. Generally in this connection one also speaks of latent catalysts, and, in the thermal case, of thermolatent catalysts. These catalysts are idle until the reaction mixture reaches a certain temperature. Above this temperature they are then active, preferably instantaneously active. These latent catalysts enable long pot lives and fast demoulding-times.
The class of latent catalysts that has been known hitherto and used where appropriate consists of mercury compounds. The most prominent representative of these is phenylmercury neodecanoate (Thorcat 535 and Cocure 44). This catalyst reveals a latent reaction profile, the catalyst being virtually inactive initially and becoming instantaneously active at a certain temperature (usually around 70° C.) only after slow heating of the mixture, usually by reason of the exothermic nature of the uncatalysed conversion of NCO groups with OH groups. When this catalyst is employed, very long open-times with very short curing-times can be achieved. This is particularly advantageous when a great deal of material has to be discharged (for example, a large mould has to be filled) and the reaction is to be terminated rapidly and hence economically after discharge has taken place.
When latent catalysts are used, it is particularly advantageous if, in addition, the following conditions are satisfied:    a) An increase in the catalyst quantity accelerates the reaction without the catalyst losing latency.    b) A lowering of the catalyst quantity slows down the reaction without the catalyst losing latency.    c) A variation of the catalyst quantity, of the index, of the mixing ratio, of the output quantity and/or of the proportion of hard segment in the polyurethane does not impair the latency of the catalyst.    d) In all the aforementioned variations, the catalyst provides for a virtually complete conversion of the reactants without tacky places being left behind.
A particular advantage of the latent catalysts can be seen in the fact that, as a consequence of their diminishing catalytic action with falling temperature, they accelerate the dissociation of urethane groups in the finished polyurethane material, at room temperature for example, only a little in comparison with conventional catalysts. Consequently they contribute to favourable continuous-use properties of the polyurethanes.
Furthermore, when catalysts are employed care generally has to be taken to ensure that the physical properties of the products are, as far as possible, not influenced negatively. This is also the reason why a targeted catalysis of a certain reaction is so important. Precisely in the preparation of elastomers, particularly of casting elastomers, the use of mercury catalysts is very widespread, since they are widely employable, do not have to be combined with additional catalysts, and catalyse the reaction between OH groups and NCO groups very selectively. The only—though very significant—drawback is the high toxicity of the mercury compounds, so great efforts are being made to find alternatives to the mercury catalysts. Furthermore, these compounds are prohibited in some industries (automobile industry, electrical industry).
A survey of the state of the art is given in WO 2005/058996. Here it is described how working proceeds with titanium and zirconium catalysts. Numerous possible combinations of various catalysts are also mentioned.
Although systems that are at least less toxic than mercury catalysts—for example, based on tin, zinc, bismuth, titanium or zirconium, but also amidine and amine catalysts—are known on the market, they have not hitherto exhibited the robustness and simplicity of the mercury compounds.
Certain combinations of catalysts cause the gel reaction to take place very largely separately from the curing reaction, since many of these catalysts act only selectively. By way of example, bismuth(III) neodecanoate is combined with zinc neodecanoate and neodecanoic acid. Often 1,8-diazabicyclo[5.4.0]undec-7-ene is additionally added. Although this combination pertains to the most well-known, it is unfortunately not so widely and universally employable as, for example, Thorcat 535 (Thor Especialidades S.A.) and is furthermore susceptible in the event of fluctuations in the formulation. The use of these catalysts is described in DE 10 2004 011 348. Further combinations of catalysts are disclosed in WO 2005/058996, U.S. Pat. Nos. 3,714,077, 4,584,362, 5,011,902, 5,902,835 and 6,590,057.
In the case of the product DABCO DC-2,produced by Air Products Chemicals Europe B.V., which is available on the market, it is a question of a catalyst mixture consisting of 1,4-diazabicyclo[2.2.2]octane (DABCO) and dibutyltin diacetate. The disadvantage of this mixture is that the amine acts in activating manner immediately. Alternative systems are, for example, POLYCAT SA-1/10 (Air Products Chemicals Europe B.V.). In this case, it is a question of DABCO that is blocked with acid. Although this system is thermolatent, systems of such a type are not used, on account of their poor catalytic action in the course of curing; the elastomers that are produced in the presence of these systems remain tacky at the end of the reaction; one also speaks of the ‘starving’ of the reaction.
The object was therefore to make available systems and catalysts with which it is possible to prepare polyisocyanate polyaddition products having good mechanical properties and which initially provide a greatly delayed reaction and, after this initial phase, an accelerated reaction to yield the end product. The system and the catalyst should, in addition, be free from toxic heavy metals such as cadmium, mercury and lead.
This object was surprisingly able to be achieved through the use of special Sn(IV) catalysts.